Delage said Oxfam's relief assessment showed the island had only limited medical facilities. He said the group was planning to start shipping in supplies on Wednesday. "The hospital has been quite heavily damaged, and its staff is out looking for relatives," he said. "There is one nurse and one doctor. We have provided them with basic medical supplies."
In Sibolga, a city in western Sumatra on the Indian Ocean, relief workers and residents gathered at the port in efforts to reach Nias.
Haogombowo sits with the body of his wife at a makeshift morgue on Indonesia's Nias Island, where Monday's earthquake killed hundreds.
(Suzanne Plunkett -- AP)
Photo Gallery: Hundreds were killed after a powerful underwater earthquake struck Indonesia.
"I'm very worried because I heard that my village is destroyed and I have no idea what's happened to my family," said Yusaroh Bule, 26, whose wife and children were in Nias. As he spoke, he was leaning out the window of a boat packed with people as it prepared to leave for the island. He was traveling with his sick mother, his younger brother and sister.
Jamis Arnek, 18, was sitting with 25 fellow Boy Scouts from Nias who were on a camping trip in the Sibolga hills when they heard about the earthquake. They were trying to return home. "We're afraid and anxious and don't know what's happened to our families," he said, looking distraught.
Panic gripped Nias during the earthquake and in the hours afterward. A mosque in Gunungsitoli is serving as a refuge for the homeless and a staging point for rescue efforts.
During the December rescue effort, mosques in the affected area of Sumatra around Banda Aceh, the provincial capital, also became shelters, having survived on a shoreline that had been stripped clean by giant ocean waves.
Delage said some residents were bringing bodies to the mosque and preparing them for burial. "The situation is calm, people have calmed down," he said. "Obviously, the population is heavily traumatized."
With many unanswered questions about the degree of destruction and loss of life, officials were also analyzing why the quake had not generated a tsunami.
Monday's quake was smaller than the December temblor, which had a magnitude of 9.0, but both are among the 10 strongest earthquakes in the past 100 years.
Staff writer Glenn Kessler in Washington and special correspondent Yayu Yuniar in Sibolga contributed to this report.